The invention relates to a method of application of a liquid or pasty medium onto a moving material web and to an apparatus for implementing the method.
A method as well as an apparatus of this type are known from DE 44 15 581 C2. A coating medium is directly or indirectly applied by an application means onto a moving material web. After passing the application unit, the material web is initially moved along a straight path of movement of the web where one or more contactless drying means are directed onto the material web. Subsequently, the moving material web is deflected about the shell surface of a rotatable deflection roll, an air cushion being formed between the shell surface of the roll and the material web so that the material web is deflected without making contact.
A mode of application is denoted by the term "direct application" of a liquid or pasty medium when an application means directly applies the coating medium, the latter being supported on a counter-surface which, for example, is in the form of a rotatable counter-roll or a moving endless belt. An application mode is denoted by the term "indirect application" of a liquid or pasty medium when the coating medium is initially applied onto an application surface such as the shell surface of an application roll and then transferred onto and pressed into the material web from this location in a roll gap through which the material web is guided.
An apparatus is described in the published patent application DE 44 16 399 A1 in which a coating medium is initially pressed into the moving material web in a roll gap by means of an indirect application means and then, after passing a straight path of movement of the web, this moving material web is deflected contactlessly on an air cushion over a stationary deflection means into a new direction of movement of the web.
In apparatus of the previously described kind, particularly when the coating medium is directly applied onto the material web, i.e. not pressed into it, it is possible that a throwing out of the applied coating medium occurs during the contactless deflection. This leads to an uneven coating of the material web. Further, a satisfactory uniformity of the applied film of coating medium is not sufficiently guaranteed.
In this regard, it is suggested in the published patent application DE 44 29 964 A1, after the application of an excess of coating medium, to guide the moving material web in such a concavely curved manner, at least along a partial stretch up to a scraping means at which the excess coating medium is scrapped off, that centrifugal forces act in the direction towards the web. In this manner, a spattering of coating material and an uneven coating of the coating medium are avoided and, by means of the centrifugal forces, a evening out of the applied film of coating medium is to be effected.